Originally posted by Rondec If you have a D700 (12 megapixels) and a K5, there is no cropping the D700 to equal the K5 image, even if the K5 image is really just a crop of the D700 image.
That is right, but look at the trend:
Previous generation:
FF had: 12MP (D700), 21MP (5DII) - top: 21MP
APS-C had: 16MP (K-5), 18MP (60D, 7D) - top: 18MP
ratio: 21/18 = 1.17
This generation:
FF has: 36MP (D800), 22MP (5DIII), 24MP (A99) - top: 36MP
APS-C is improved with the 24MP APS-C sensor but most cameras are still 16-18MP - top: 24MP
ratio: 36/24 = 1.5
The ratio is increasing. It will get proportional to the sensor area in one or two more generations of FF sensors.
To simplify calculations, I will use a factor of 2 for the surface difference between the formats (I know it's a bit more but I'm too lazy to pull a calculator).
D800's 36MP gives 18MP with an APS-C crop. Yes, 24MP cameras offer more, but that is just 30% more resolution, which is less than the jump we had for APS-C from 10MP in K10D to 15MP in K-7 - and I cannot say that that resolution jump has necessarily made my K-7 shots much better. With the D700 it was tricky - cropping to APS-C would give you just a measly 6MP - yes, the "reach" argument made sense there. Now, even the 5DIII provides 12MP in an APS-C crop - that is plenty of resolution for professional work. Even if FF sensors won't get similar densities as APS-C ones - not because of technical reasons, but because of economical ones, their resolution is high enough that it just won't matter anymore.